Heat conductive mold and manufacturing method thereof

ABSTRACT

A heat conductive mold is provided in which boron nitride powder has a magnetic field which is oriented in a fixed direction within a polymer. The polymer is preferably at least one selected from silicon rubber, epoxy, Polyimide and polyurethane. The content of the boron nitride powder is from twenty-two 400 weight parts to 100 weight parts ofpolymer. A method is also provided in which a heat conductive mold of excellent heat conductivity is provided. The method includes impressing a magnetic field to the polymer composition containing boron nitride powder. The magnetic field impressed on the boron nitride powder, in the composition is impressed to have a fixed direction. The field is set after the direction is established. As an alternative, the method may include pressing the magnetic field to the polymer composition including the boron nitride powder and also a solvent.

FIELD OF THE INVENTION

[0001] The present invention concerns a heat conductive mold of goodheat conductivity and manufacturing method thereof.

PRIOR ARTS

[0002] Recently, measures against the heat generated from electronicapparatuses are becoming an important issue by the high densityimplementation of semi-conductor package or higher integration andspeed-up of LSI, following the performance enhancement, miniaturization,and weight reduction of electronic apparatuses. Ordinarily, in order todissipate heat from heating devices, method to use printed circuitboards made of good heat conductive metals or ceramics, method to form athermal veer hole to radiate heat in the substrate, method to use goodheat conductive metals, ceramics or resins as semiconductor packagematerial, method to interpose highly heat conductive grease or flexibleheat conductive rubber sheet for the purpose of reducing the contactheat resistance between the heat source and the radiator, or between theheat source and the metallic heat conductive plate, method to usecooling fan, heat pipe or heat dissipation plate, or others are publiclyknown.

[0003] As such heat conductive mold requiring good thermal conductivity,molds filled with highly heat conductive aluminum oxide, boron nitride,aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, quartz,aluminum hydroxide or other metal oxides, metal nitrides, metalcarbides, metal hydroxides or other electric insulation fillers are usedin practice.

[0004] However, flake form boron nitride powder could not deploy enoughits heat conductivity in case of sheet-shaped mold where boron nitridepower is simply diffused in polymer, because its heat conductivity inthe flake thickness direction is lower than the heat conductivity in thesurface direction, and the flake is filled with its surface direction inparallel with the sheet thickness direction. Therefore, various methodshave been proposed to orient flake form boron nitride powder verticallyin the thickness direction of the sheet-shaped mold.

[0005] To be more specific, the heat conductive insulation sheetdisclosed in the Japanese Patent Publication SHOU 62-154410 is a heatconductive insulation sheet made of organo-poly-siloxane and boronnitride powder specifying X-ray diffraction characteristics in the sheetthickness direction, and realized by a method using specific boronnitride powder and a manufacturing method applying a compositionincluding boron nitride powder by ultrasonic commotion.

[0006] The Japanese Patent Publication HEI 3-151658 is a heat radiationsheet where boron nitride powder is oriented upright in the thicknessdirection of the sheet, manufactured by a method for thrusting theextruded sheet, or the compression orientation method.

[0007] The Japanese Patent Publication HEI 8-244094 discloses amanufacturing method for charging flake-shaped particles vertically inthe thickness direction of the sheet by the extrusion molding method,the Japanese Patent Publication HEI 11-77795 and the Japanese PatentPublication HEI11-156914 a continuous manufacturing method of rubbersheet for charging boron nitride powder vertically in the thicknessdirection of the sheet by the extrusion molding method using a die ofparticular structure.

[0008] However, the manufacturing method illustrated in the JapanesePatent Publication SHOU 62-154410 requires ultrasonic commotion machineor other special equipment or treatment processes, or use of specificboron nitride powder making the method inconvenient.

[0009] All of methods disclosed in the Japanese Patent Publication HEI3-151 658, Japanese Patent Publication HEI 8-244094, Japanese PatentPublication HEI 11-77795 and Japanese Patent Publication HEI 11-156 914use flake form boron nitride powder or the like, require dies ofcomplicated structure or extrusion molding equipment and complicatedprocessing operations, and they were not necessarily simplemanufacturing methods.

[0010] On the other hand, the Japanese Patent Publication Laid-Open No.HEI 11-87483 by the Applicant orients diamagnetic filler of 20Weight/m·Kor more in thermal conductivity in a constant direction in polymer;however, boron nitride powder was not taken into account as diamagneticmaterial.

SUMMARY OF THE INVENTION

[0011] To solve these problems, we have studied seriously and found thata heat conductive mold characterized by that boron nitride powder isfield oriented in a constant direction in polymer presents a good heatconductivity, a method to manufacture easily a heat conductive mold ofgood thermal conductivity applying the nature of boron nitride powder toorient along the magnetic power line in a magnetic field, and attainedthe present invention.

[0012] Namely, the present invention concerns a heat conductive moldcharacterized by that boron nitride powder is field oriented in aconstant direction in polymer, a manufacturing method of heat conductivemold characterized by that boron nitride powder is field oriented in aconstant direction in a composition by impressing magnetic field to apolymer component including boron nitride powder, and a manufacturingmethod of heat conductive mold characterized by that boron nitridepowder is field oriented in a constant direction in a composition byimpressing magnetic field to a liquid polymer component including boronnitride powder and solvent, and set after having removed the solvent.

[0013] Boron nitride powder used in the present invention is notparticularly specified as for the kind of crystalline system, shape orsize of powder particle, aggregation rate of powder particle, or theirdistribution. Concerning the crystalline system, boron nitride powder ofhexagonal system, cubic system or other structures can be used.Particularly, highly crystalline boron nitride powder of hexagonalsystem or cubic system is preferable, because of its excellent thermalconductivity.

[0014] The particle form of boron nitride powder is not limited to flakeform or flat form, but also various other forms of boron nitride powder,such as granular, massive, spherical, fiber, whisker form boron nitridepowder, or ground product thereof can be used. The particle diameter ofboron nitride powder is not specified; however, individual averageprimary diameter in the range of 0.01˜100 μm, and more preferably, inthe range of 1˜50 μm can be used. Under 0.01 μm, it is difficult tocharge in quantity, and boron nitride powder larger than 100 μm isdifficult to produce, and disadvantageous in terms of price. As for theflake form boron nitride powder, it is practical to use within the rangeof 1˜1 60 μm in its maximum diameter, because it can easily be blendedwith polymer and field oriented. Further, boron nitride powder having astructure where primary particles are aggregated can be used.

[0015] In particular, the present invention is basically different froma conventional manufacturing method of mechanical orientation usingboron nitride powder an-isotropic shape and is hardly influenced by theboron nitride powder shape, because it can be field oriented in a way toincrease the heat conductivity using the magnetic anisotropy proper tothe boron nitride powder.

[0016] The quantity of boron nitride powder to be contained in polymeris preferably 20˜400 weight parts to 100 weight parts of polymer. Lessthan 20 weight parts, the improvement effect of heat conductivity issmall, while the content more than 400 weight parts increases thecomposition viscosity, reduces the fluidity, making the moldingdifficult and bubble inclusion inevitable, so it is not appropriate.More preferably, boron nitride powder is added by 30˜300 weight parts,and still preferably, by 40˜250 weight parts. Higher concentrations mayalso be obtained by using boron nitride powders of different particlediameter, or by surface treatment.

[0017] The kind of polymer used for the present invention is notparticularly limited. According to the shape, hardness, mechanicalnature, thermal nature, electric nature, durability, reliability orother required performances, thermoplastic resins, thermoplasticelastomers, setting resins, reticulated rubbers, or the like can beselected. Polymer used for charging boron nitride powder at a highconcentration, polymers and polymer precursors presenting low viscosityin liquid or melt state. Also, it is preferable to reduce the viscosityof polymers or polymer precursors by dissolving with solvent, in orderto increase the concentration of boron nitride powder, or to acceleratethe field orientation of boron nitride powder in the magnetic fieldatmosphere.

[0018] Thermoplastic resins or thermoplastic elastomers used as polymerinclude polyethylene, polypropylene, ethylene propylene copolymer orother ethyleneaolefin copolymer, polymethylpentene, PVC, polyvinylidenechloride, polyvinyl acetate, ethylene vinylacetate copolymer, polyvinylalcohol, polyvinylacetal, polyvinylidene fluoride andpolytetrafluoroethylene or other fluoric resins, polyethyleneterephthalate, polystyrene, polyacrylonitrile, styrene acrylonitrilecopolymer, ABS resin, polyphenylene ether and degenerated PPE resin,aliphatic and aromatic polyamides, polyimide, polyamide-imide,polymethacrylic acid and its methylester or other polymethacrylic acidesters, polyacrylic acids, polycarbonate, polyphenylene sulfide,plysulfone, polyether sulfone, polyether nitrile, polyether ketone,plyketone, liquid crystal polymer, silicone resin, ionomer or otherthermoplastic resins, styrene butadiene or styrene isoprene bloccopolymer and their hydrogenated polymer and styrene base thermoplasticelastomers, olefin base thermoplastic elastomers, PVC base thermoplasticelastomers, polyester base thermoplastic elastomers, polyurethane basethermoplastic elastomers, polyamide base thermoplastic elastomers, orother thermoplastic elastomers.

[0019] Thermosetting resins and reticulated rubbers include epoxy,polyimide, bismuth imide, benzocyclo butene, phenol, unsaturatedpolyester, diallyl phtalate, silicone, polyurethane, polyimide silicone,thermosetting type polyphenylene, ether resin and degenerated PPE resin,natural rubber, butadiene rubber, isoprene rubber, styrene butadienecopolymer rubber, nitrile rubber, hydrogenated nitrile rubber,chloroprene, ethylene propylene rubber, chlorinated polyethylene,chlorosulphonated polyethylene, butyl rubber and butyl rubber halide,fluoric rubber, urethane rubber, silicone rubber or other reticulatedrubber.

[0020] The heat conductive mold of the present invention usespreferably, at least one of these polymers selected from siliconerubber, epoxy, polyurethane, unsaturated polyester, polyimide, bismuthimide, benzocyclobutene, fluoric resin, and polyphenylene ether resin,and more preferably, at least one of these polymers selected fromsilicone rubber, epoxy, polyimide and polyurethane in terms of heatresistance, and electric reliability. Moreover, these polymers can be alow viscosity liquid for blending with boron nitride powder and canreduce the viscosity when heat melted, and when magnetic field isimpressed, boron nitride powder is oriented easily.

[0021] For wiring board application or the like requiring low dielectricconstant, dielectric tangent and characteristics in high frequencyrange, fluoric resin or thermosetting type polyphenylene ether resin ordegenerated PPE resin, polyolefin base resin are preferable. Further,polymer alloy made of a plurality of polymers selected from thesepolymers may also be used. The reticulation method of thermosettingresin or reticulated rubber is not limited to thermosetting, butpolymers by publicly known reticulation methods such as photo-setting,hygro-setting, or the like may also be used.

[0022] The heat conductive mold of the present invention may be usedwith a small amount of other heat conductive filler of spherical,powder, fiber, needle, flake or whisker form filler made of highlyconductive aluminum oxide, aluminum nitride, zinc oxide, siliconcarbide, aluminum hydroxide or other metal oxides, metal nitrides, metalcarbides, metal hydroxides or metals, alloys, carbon, graphite, anddiamond.

PREFERRED EMBODIMENTS OF THE INVENTION

[0023] The manufacturing method of heat conductive mold of the presentinvention characterized by that boron nitride powder is field orientedin a constant direction in a polymer is characterized by that boronnitride powder in a composition is oriented and set in a constantdirection in a composition by impressing magnetic field to a polymercomponent including boron nitride powder. Further, it is characterizedby that boron nitride powder in the composition is oriented in aconstant direction in a composition by impressing magnetic field to apolymer component including boron nitride powder and solvent, and setafter having removed the solvent.

[0024] It is possible to orient boron nitride powder in a polymercomposition in a fixed direction along the magnetic power line, byimpressing exterior magnetic field to the composition, using theanisotropy of magnetic susceptibility of boron nitride powder, and toobtain a heat conductive mold whose heat conductivity in the fixeddirection is extremely enhanced. For example, in order to align boronnitride powder in the thickness direction of sheet-shaped heatconductive mold, N pole and S pole of permanent magnet or electromagnetare opposed in the thickness direction, and disposed so that themagnetic power line corresponds to the desired orientation direction ofboron nitride powder (FIG. 5). On the other hand, in order to enhancethe heat conductivity in a fixed direction in the vertical direction andin the transversal direction or in the vertical and transversalhorizontal directions in a plane of sheet-shaped heat conductive mold,boron nitride powder can be oriented aligned in the direction in theplane by opposing the magnet N pole and S pole vertically to thethickness direction (FIG. 6). Otherwise, boron nitride powder can alsobe aligned in the direction in the plane by opposing the magnet N poleand N pole, or S pole and S pole in the thickness direction. Besides,the magnetic power line is not required to be straight line, but it maybe a curve, a rectangle, or two directions or more. For the sheet-shapedmold, it is also possible place the magnetic power line slant to thesheet thickness, to field orient the flake form boron nitride powder inthe slant direction.

[0025] The boron nitride powder magnetic field orientation method of thepresent invention is essentially different from the mechanicalorientation method of boron nitride powder using fluid field or shearingfiled of extrusion molding or press molding proposed in the prior art.In other words, it is possible to obtain a high heat conductivity byorienting boron nitride powder in an arbitrary fixed directioncorresponding to the magnetic power line direction. In addition, magnetsare not required to be opposed at both sides, but it is possible tofield orient boron nitride powder in the raw material composition by amagnet disposed only on one side.

[0026] Magnetic field generation means user as exterior magnetic fieldmay be a permanent magnet, electromagnet or coil, and a flux densityrange from 0.05 to 30 tesla can achieve a practical orientation of boronnitride powder. As the present invention used a very weak an-isotropicmagnetization rate of boron nitride powder, it is necessary to orientboron nitride powder sufficiently in a stronger magnetic filedatmosphere, and to set matrix polymer by thermosetting reaction orcooling. Preferable magnetic flux density for orientation is 0.5 teslaor more, and more preferably, 1 tesla or more.

[0027] In order to improve wetness or adhesivity between boron nitridepowder and polymer, preliminary degreasing or cleaning of the boronnitride powder surface, or surface treatment by silane base, titanebase, aluminum bas or other ordinary coupling agents facilitate furtherthe diffusion a blending of a quantity of boron nitride powder, and theobtained mold will have a higher heat conductivity.

[0028] The heat conductive mold of the present invention can be appliedto radiation plate, radiation rubber sheet, semiconductor packagecomponent, heat sink, heat spreader, case, belt, roller, tube, tape basematerial, cap, profile or the like requiring a high heat conductivity.As boron nitride powder is excellent in electric insulation, the heatconductive mold of the present invention may also be applied to thewiring substrate.

BRIEF EXPLANATION OF THE DRAWINGS

[0029]FIG. 1 shows an example of utilization of the heat conductive moldof the present invention (disposed in a gap between a ball grid arraytype semiconductor package 2 and a radiator 4);

[0030]FIG. 2 shows an example of utilization of the heat conductive moldof the present invention (disposed in a gap between a chip size typesemiconductor package 2 and a printed circuit board 1);

[0031]FIG. 3 shows an example of utilization of the heat conductive moldof the present invention (disposed in a gap between a pin grid arraytype semiconductor package 2 and a heat sink 5);

[0032]FIG. 4 shows an example of utilization of the rubber sheet shapeheat conductive mold of a first embodiment of the present invention(disposed in a gap between a plurality of heating semiconductor device 6and a case 7);

[0033]FIG. 5 shows an example of manufacturing method of the heatconductive mold of the present invention;

[0034]FIG. 6 shows another example of manufacturing method of the heatconductive mold of the present invention;

[0035]FIG. 1˜FIG. 4 show examples wherein the heat conductive mold 3obtained by the present invention is interposed between heatingsemiconductor device 2, 6 and head conductive members, such as radiator4, print circuit board 1, heat sink 5, or case 7.

[0036] Now, the present invention will be described more in detail basedon examples. In the following examples and comparison examples, the heatconductivity was evaluated through the measurement of heat resistancevalue using a transistor (made by Toshiba Corp. TO-220).

EXAMPLE 1

[0037] A composition is prepared by blending 100 weight parts of addedtype liquid silicon rubber (made by GE Toshiba Silicon, TSE3070), 80weight parts of hexagonal crystalline system flake form boron nitridepowder (Denki Kagaku Kogyo K.K., SGP average particle diameter 19 μm)and 100 weight parts of hexane as solvent. The composition is chargedinto a plate shape die of 15 mm in thickness, 20 mm in length and 20 mmin width, boron nitride powder is oriented sufficiently under themagnetic field atmosphere where N pole and S pole of 2 tesla in fluxdensity are opposed in the thickness direction, then heat dried toremove solvent hexane, and heat set, to obtain rubber sheet shape heatconductive mold of 1.5 mm in thickness. The heat resistance value of theobtained heat conductive mold was 0.26° C./W.

COMPARISON EXAMPLE 1

[0038] A composition is prepared by blending 100 weight parts of addedtype liquid silicon rubber (made by GE Toshiba Silicon, TSE3070), and 80weight parts of hexagonal crystalline system flake form boron nitridepowder (Denki Kagaku Kogyo K.K., S G P average particle diameter 19 μm).The composition is charged into a plate shape die of 15 mm in thickness,20 mm in length and 20 mm in width and heat set, to obtain rubber sheetshape heat conductive mold. The heat resistance value of the obtainedheat conductive mold was 0.38° C./W.

EXAMPLE 2

[0039] A composition is prepared by blending 100 weight parts of liquidepoxy resin (made by Three Bond Co., Ltd. TB2280C) and 180 weight partsof hexagonal crystalline system granular boron nitride powder (ShowaDenko Co., Ltd. UHP-EX average particle diameter 35 μm). The compositionis charged into a plate shape die of 15 mm in thickness, 20 mm in lengthand 20 mm in width, boron nitride powder is oriented sufficiently underthe magnetic field atmosphere where N pole and S pole of 6 tesla in fluxdensity are opposed in the thickness direction, and heat set, to obtaina hard plate shape heat conductive mold as shown in FIG. 5(1), FIG. 5(2)and FIG. 5(3). The heat resistance value of the obtained heat conductivemold was 0.21° C./W.

COMPARISON EXAMPLE 2

[0040] A composition is prepared by blending 100 weight parts of liquidepoxy resin (made by Three Bond Co., Ltd. TB2280C) and 180 weight partsof hexagonal crystalline system granular boron nitride powder (ShowaDenko Co., Ltd. UHP-EX average particle diameter 35 μm). The compositionis charged into a plate shape die of 15 mm in thickness, 20 mm in lengthand 20 mm in width, and heat set, to obtain a hard plate shape heatconductive mold. The heat resistance value of the obtained heatconductive mold was 0.32° C./W.

EXAMPLE 3

[0041] A composition is prepared by blending 100 weight parts of solidportion of polyimide varnish containing N methyl pyrrolidone as solvent(made by Ube Kosan Co., Ltd., Yupifine ST, concentration of solidportion 18.5%) and 60 weight parts of hexagonal crystalline system flakeform boron nitride powder (made by Showa Denko Co., Ltd. UHP-S1 averageparticle diameter 1 to 2 μm). The composition is charged into a box dieof 20 mm in length, 20 mm in width and 40 mm in depth, boron nitridepowder is oriented sufficiently under the magnetic field atmospherewhere N pole and S pole of 6 tesla in flux density are opposed in thethickness direction, and heat set after having removed solvent N methylpyrrolidone, to obtain a film shape heat conductive mold of 120 μm inthickness. The heat resistance value of the obtained heat conductivemold was 0.18° C./W.

COMPARISON EXAMPLE 3

[0042] A composition is prepared by blending 100 weight parts of solidportion of polyimide varnish containing N methyl pyrrolidone as solvent(made by Ube Kosan Co., Ltd., Yupifine ST, concentration of solidportion 18.5%) and 60 weight parts of hexagonal crystalline system flakeform boron nitride powder (made by Showa Denko Co., Ltd. UHP-S1 averageparticle diameter 1 to 2 μm). The composition is charged into a box dieof 20 mm in length, 20 mm in width and 40 mm in depth, and heat setafter having removed solvent N methyl pyrrolidone, to obtain a filmshape heat conductive mold of 120 μm in thickness. The heat resistancevalue of the obtained heat conductive mold was 0.27° C./W.

[0043] Comparison Example 1 Comparison Example 3 are conventional moldswherein flake form boron nitride powder is charged into polymer, andComparison Example 2 is the one wherein granular boron nitride powder ischarged, and they present a high heat resistance value. The heatconductive mold of Example 1 Example 2, Example 3 of the presentinvention are obtained by impressing magnetic field to the polymercomposition containing the same amount of flake form boron nitridepowder or granular boron nitride powder as the corresponding ComparisonExample, field orienting boron nitride powder in the composition, andthen heat setting, and it presents smaller heat resistance value andbetter heat conductivity than the Comparison Example.

[0044] As described above, the present invention allows to produce aheat conductive mold of excellent heat conductivity, by impressingmagnetic field to the polymer composition containing flake form boronnitride powder or granular boron nitride powder, field orienting boronnitride powder in the composition to a fixed direction, and then heatsetting.

[0045] Using the heat conductive mold of the present invention, variousradiation components requiring a high heat conductivity such as highheat value CPU (central processing unit) or other semiconductors, powersource, light source, plasma display, printed circuit board or the likecan be supplied.

1. A heat conductive mold, wherein boron nitride powder is magneticfield oriented to a fixed direction in a polymer.
 2. The heat conductivemold of claim 1 , wherein the polymer is at least one selected fromsilicon rubber, epoxy, polyimide and polyurethane.
 3. The heatconductive mold of claim 1 or 2 , wherein the content of boron nitridepowder is 20 to 400 weight parts to 100 weight parts of polymer.
 4. Amanufacturing method of heat conductive mold of excellent heatconductivity, by impressing magnetic field to the polymer compositioncontaining boron nitride powder, field orienting boron nitride powder inthe composition to a fixed direction, and then setting the same.
 5. Amanufacturing method of heat conductive mold of excellent heatconductivity, by impressing magnetic field to the polymer compositioncontaining boron nitride powder and solvent, field orienting boronnitride powder in the composition to a fixed direction, and then settingthe same after having removed the solvent.